Airbags for motor vehicles are known and have been used for a substantial period of time. A typical construction material for airbags has been a polyester or nylon fabric, coated with an elastomer such as neoprene, or silicone. The fabric used in such bags is typically a woven fabric formed from synthetic yarn by weaving practices which are well known in the art.
The coated material has found acceptance because it acts as an impermeable barrier to the inflation medium. This inflation medium is generally a nitrogen gas generated from a gas generator or inflator. Such gas is conveyed into the cushion at a relatively warm temperature. The coating obstructs the permeation of the fabric by such hot gas, thereby permitting the cushion to rapidly inflate without undue decompression during a collision event.
Airbags may also be formed from uncoated fabric which has been woven in a manner that creates a product possessing low permeability or from fabric that has undergone treatment such as calendering to reduce permeability. Fabrics which reduce air permeability by calendering or other mechanical treatments after weaving are disclosed in U.S. Pat. No. 4,921,735; U.S. Pat. No. 4,977,016; and U.S. Pat. No. 5,073,418 (all incorporated herein by reference).
The coating of a fabric with an elastomer such as neoprene typically requires the application of that elastomer from a solution in a volatile solvent. This solvent must then be evaporated and the elastomeric system cured. Typical dry coating weights for neoprene have been in the range of about 1 ounce per square yard or greater. Silicone coatings typically utilize either solvent based or complex two component point of application reaction systems. Dry coating weights for silicone have been in the range of about 0.7 ounces per square yard or greater. As will be appreciated, high add on weights substantially increase the cost of the base fabric for the airbag as well as making the eventual sewing of the fabric into an airbag structure more difficult.
The use of certain polyurethanes as coatings as disclosed in U.S. Pat. No. 5,110,666 to Menzel et al. (incorporated by reference) permits low add on weights reported to be in the range of 0.1 to 1 ounces per square yard but the material itself is relatively expensive and is believed to require relatively complex compounding and application procedures due to the nature of the coating materials. It will, of course, be readily appreciated that complex solvent-based curing systems generally add expense to the process due to the need to closely control the curing operation.
In light of the background above, it can be readily seen that there exists a need for an airbag base fabric which provides controlled low permeability through use of a coating which provides an effective barrier to air permeability while nonetheless avoiding the inherent complexity and cost of materials which have heretofor been utilized. The present invention is believed to address these and other needs through use of a coating in the form of a water borne dispersion of finely divided polyamide which can be effectively applied at dry coating weights of about 0.6 ounces per square yard or less across a polyester or nylon substrate. Other objects and advantages of the invention will become apparent upon reading the following detailed description.
While the invention will be described and disclosed in connection with certain preferred embodiments and practices, it is in no way intended to limit the invention to those specific embodiments, rather it is intended to cover equivalent structures structural equivalents and all alternative embodiments and modifications as may be defined by the scope of the appended claims and equivalence thereto.